Striving to salvage ties amid a fierce dispute over Syria, the United States and Russia on Wednesday agreed to work together on an international investigation of a Syrian chemical weapons attack last week that prompted retaliatory American missile strikes. Washington blames Russia's ally, Syrian President Bashar Assad, while Moscow says Syrian rebels are responsible.

After a day of discussions with U.S. Secretary of State Rex Tillerson, Russian Foreign Minister Sergey Lavrov said the former Cold War foes agreed a probe of events in northern Syria on April 4 was necessary. More than 80 people were killed in what the U.S. has described as a nerve gas attack that Assad's forces undoubtedly carried out. Russia says rebels dispersed whatever chemical agent was found, which the Trump administration calls a disinformation campaign.

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The news conference came after Russian President Vladimir Putin met the top American diplomat for almost two hours to see if they could rescue relations between the world's mightiest military powers. Russia's alleged meddling in the U.S. presidential election also hovered over the first face-to-face encounter between Putin and a Trump administration Cabinet member.

"There is a low level of trust between our two countries," Tillerson said candidly.

He said working groups would be established to improve U.S.-Russian ties and identify problems. He said the two sides would also discuss disagreements on Syria and how to end the country's six-year civil war.

But such hopes appeared optimistic as the diplomats outlined their sharply diverging views on Syria. Until the chemical attack, the Trump administration had sought to step back from the U.S. position that Assad should leave power. But Tillerson repeated the administration's new belief that "the reign of the Assad family is coming to an end."

Tillerson said Syria's government had committed more than 50 attacks using chlorine or other chemical weapons over the duration of the conflict. And he suggested that possible war crimes charges could be levied against the Syrian leader. Russia has never publicly acknowledged any such attack by Assad's forces and has tried for the past 18 months to help him expand his authority in Syria.

The civil war is separate from the U.S.-led effort against the Islamic State group in the north of the country.

While most immediate, U.S.-Russian dispute concerned culpability for the chemical weapons, broader disagreements over everything from Ukraine to Russia's support for once-fringe candidates in European elections were among other sore points.

Steeped in geopolitical intrigue, the meeting between Putin and Tillerson wasn't formally confirmed until the last minute, following days of speculation about whether the Russian would refuse to grant the former oil executive an audience. Putin's decision to host Tillerson signaled Moscow's intent to maintain communication with the U.S. even as the countries bash each other publicly in louder and louder tones.

The men know each other well from Tillerson's days as Exxon Mobil CEO. Putin had even honored Tillerson a friendship award.

Still, Tillerson was greeted frostily in the Russian capital as Lavrov began their meeting Wednesday by demanding to know America's "real intentions."

"We have seen very alarming actions recently with an unlawful attack against Syria," Lavrov said, referring to the 59 Tomahawk missiles Trump launched at a Syrian air base to punish Assad for using chemical weapons. "We consider it of utmost importance to prevent the risks of replay of similar action in the future."

Trump and others have indeed threatened similar action. But in a Fox Business Network interview, the U.S. president said he wouldn't intervene militarily against Assad unless the Syrian leader resorts to using weapons of mass destruction again. "Are we going to get involved with Syria? No," Trump said. But, he added, "I see them using gas ... we have to do something."

Only weeks ago, it appeared that Trump, who praised Putin throughout the U.S. election campaign, was poised for a potentially historic rapprochement with Russia. Any expectations of an easy rapport have crashed into reality amid the nasty back-and-forth over Syria and ongoing U.S. investigations into Russia's activity connected to the U.S. presidential election.

Allegations of collusion between Russian officials and Trump campaign associates also have weakened Trump's ability to sweeten any offer for greater cooperation, such as by easing economic sanctions on Moscow related to its 2014 annexation of Ukarine's Crimea region and support for pro-Russian separatists in eastern Ukraine.

Trump even criticized Putin on Wednesday, something he has largely left to top aides over the last several days.

"Frankly, Putin is backing a person that's truly an evil person," Trump said, referring to Assad. "I think it's very bad for Russia. I think it's very bad for mankind."

Of Assad, Trump added: "This is an animal."

Putin, whom U.S. intelligence agencies say tried to help Trump get elected, insisted that relations with the U.S. had only gone downhill since Trump took office in January.

"The level of trust at the working level, especially at the military level, has not become better but most likely has degraded," Putin said in an interview broadcast Wednesday by state television channel Mir.